# Exercises - Force and Motion 8

1. A girl weighing 400 N takes 4 s to run up a staircases of height 15m. How much potential energy does she gain ?
1. 6,000 J
2. 60,000 J
3. 2,400 J
4. 24,000 J

2. When a moving object is stopped due to friction, its kinetic energy is converted into
1. potential energy
2. heat energy
3. mechanical energy

3. A ball of 1kg mass is released from a height of 5m. What is the kinetic energy possessed by the ball at the height of 2m? (Ignore the energy loss due to the air resistance)
1. 150 J
2. 100 J
3. 250 J
4. 50 J
5. 200 J

4. The figure shows a ball is thrown from a building of height 10m. Find the speed of the ball right before it hit the ground.
1. 15 ms-1
2. 10 ms-1
3. 5 ms-1
4. 20 ms-1

5. Which of the followings are the unit of power?
1. J
2. W
3. J/s
4. Nm

6. A lizard of mass 2kg climbed a tree from the ground to a height of 5m in 25s. Find the power of  the lizard in this action.
1. 4 W
2. 5 W
3. 100 W
4. 50 W

7. A pile driver can lift a pile head of mass 200kg to a height of 10m in 20s. During this time, 40 kJ of electrical energy is supplied to the pile driver. Find the efficiency of the motor.
1. 50%
2. 80%
3. 100%
4. 65%